1. Field of the Invention
The present invention relates to xyloglucanases belonging to family 44 of glycosyl hydrolases, preferably to enzymes exhibiting xyloglucanase activity as their major enzymatic activity in the neutral and alkaline pH ranges; to a method of producing such enzymes; and to methods for using such enzymes in the textile, detergent and cellulose fiber processing industries.
2. Description of Related Art
Xyloglucan is a major structural polysaccharide in the primary (growing) cell wall of plants. Structurally, xyloglucans consists of a cellulose-like beta-1,4-linked glucose backbone which is frequently substituted with various side chains. The xyloglucans of most dicotyledonous plants, some monocotyledons and gymnosperms are highly branched polysaccharides in which approx. 75% of the glucose residues in the backbone bear a glycosyl side chain at O-6. The glycosyl residue that is directly attached to the branched glucose residue is invariably alpha-D-xylose. Up to 50% of the side chains in the xyloglucans contain more than one residue due to the presence of beta-D-galactose or alpha-L-fucose-(1-2)-beta-D-galactose moieties at O-2 of the xylose residues (C. Ohsumi and T. Hayashi, 1994, Plant and Cell Physiology 35: 963-967; McDougall and Fry, 1994, Journal of Plant Physiology 143: 591-595; Acebes et al., 1993, Phytochemistry 33: 1343-1345). On acid hydrolysis, the xyloglucan extracted from cotton fibers yielded glucose, xylose, galactose and fucose in the ratio of 50:29:12:7 (Hayashi et al., 1988).
Xyloglucans produced by solanaceous plants are unusual in that typical only 40% of the beta-1,4-linked glucose residues bear a glycosyl side chain at O-6. Furthermore, up to 60% of the xylose residues are substituted at O-2 with alpha-L-arabinose residues and some solanaceous plants, such as potato, also have xyloglucans with beta-D-galactose substituents at O-2 of some of the xylose residues (York et al., 1996).
Xyloglucan is believed to function in the primary wall of plants by cross linking cellulose-micro fibrils, forming a cellulose-xyloglucan network. This network is considered necessary for the structural integrity of primary cell walls (Carpita et al., 1993). Another important function of xyloglucan is to act as a repository for xyloglucan subunit oligo saccharides that are physiologically active regulators of plant cell growth. Xyloglucan subunits may also modulate the action of a xyloglucan endotransglycosylase (XET), a cell wall associated enzyme that has been hypothesized to play a role in the elongation of plant cell walls. Therefore xyloglucan might play an important role in wall loosening and consequently cell expansion (Fry et al., 1992).
The seeds of many dicotyledonous species contain xyloglucan as the major polysaccharide storage reserve. This type of xyloglucan, which is localized in massive thickenings on the inside of the seed cotyledon cell wall, is composed mainly of glucose, xylose and galactose (Rose et al., 1996).
Seeds of the tamarind tree Tamarindus indica became a commercial source of gum in 1943 when the gum was found useful as a paper and textile size. Sizing of jute and cotton with tamarind xyloglucan has been extensively practiced in Asia owing to the low cost of the gum and to its excellent properties. Food applications of tamarind xyloglucan include use in confections, jams and jellies and as a stabilizer in ice cream and mayonnaise (Whistler et al., 1993).
Xyloglucanase activity is not included in the classification of enzymes provided by the Enzyme Nomenclature (1992). Hitherto, this enzymatic activity has simply been classified as glucanase activity and has often been believed to be identical to cellulolytic activity (EC 3.2.1.4), i.e., activity against beta-1,4-glycosidic linkages in cellulose or cellulose derivative substrates, or at least to be a side activity in enzymes having cellulolytic activity. However, a true xyloglucanase is a true xyloglucan specific enzyme capable of catalyzing the solubilization of xyloglucan to xyloglucan oligosaccharides but which does not exhibit substantial cellulolytic activity, e.g., activity against the conventionally used cellulose-like substrates CMC (carboxymethylcellulose), HE cellulose and Avicel (microcrystalline cellulose). A xyloglucanase cleaves the beta-1,4-glycosidic linkages in the backbone of xyloglucan.
Xyloglucanase activity is disclosed in Vincken et al. (1997) wherein three different endoglucanases EndoI, EndoV and EndoVI from Trichoderma viride (similar to T. reesei) are characterized. EndoI, EndoV and EndoVI belong to families 5, 7 and 12 of glycosyl hydrolases, respectively, see Henrissat, B. et al. (1991, 1993).
WO 94/14953 discloses a family 12 xyloglucanase (EG II) cloned from the fungus Aspergillus aculeatus and expressed in the fungus Aspergillus oryzae. 
WO 99/02663 discloses xyloglucanases cloned from Bacillus licheniformis (family 12) and Bacillus agaradhaerens (family 5) and expressed in Bacillus subtilis. 
It is an object of the present invention to provide an enzyme with a high xyloglucanase activity at an alkaline pH which xyloglucanase exhibits excellent performance in conventional detergent compositions.